A Narrative Review on the Effectiveness of Bone Regeneration Procedures with OsteoBiol® Collagenated Porcine Grafts: The Translational Research Experience over 20 Years

Over the years, several bone regeneration procedures have been proposed using natural (autografts, allografts, and xenografts) and synthetic (i.e., metals, ceramics, and polymers) bone grafts. In particular, numerous in vitro and human and animal in vivo studies have been focused on the discovery of innovative and suitable biomaterials for oral and maxillofacial applications in the treatment of severely atrophied jaws. On this basis, the main objective of the present narrative review was to investigate the efficacy of innovative collagenated porcine bone grafts (OsteoBiol®, Tecnoss®, Giaveno, Italy), designed to be as similar as possible to the autologous bone, in several bone regeneration procedures. The scientific publications were screened by means of electronic databases, such as PubMed, Scopus, and Embase, finally selecting only papers that dealt with bone substitutes and scaffolds for bone and soft tissue regeneration. A total of 201 papers have been detected, including in vitro, in vivo, and clinical studies. The effectiveness of over 20 years of translational research demonstrated that these specific porcine bone substitutes are safe and able to improve the biological response and the predictability of the regenerative protocols for the treatment of alveolar and maxillofacial defects.


Introduction
Bone regeneration procedures are surgical techniques developed to restore the jaw defects provoked by tissue damage, infections, tooth loss, neoplasms, or local trauma [1][2][3]. Many different protocols have been adopted in accordance with the defect type (horizontal/vertical augmentation) [4][5][6][7], the local anatomy (anterior/posterior region of maxilla/mandibula) [8][9][10][11], the defect extension, and the planned rehabilitation [4,[12][13][14]. The rationale of these procedures is to obtain a durable regeneration of the hard/soft tissue interface after the organization of a blood clot, which promotes the local new bone formation [15][16][17]. The use of xenografts and alloplastic bone substitutes represents a useful and A total of 1375 manuscripts have been detected by the electronic database research A total of 266 duplicates have been removed, and 1109 papers have been considered fo the full-text eligibility evaluation. A total of 44 literature reviews, five book chapters, 8 papers written in non-English grammar, and 772 off-topic manuscripts were excluded. I the end, a total of 201 papers have been included in the final analytical synthesis (Figur 1).

Description of the Porcine Grafts
Figures 2 and 3 report the characteristics and the clinical applications of the differen biomaterials (OsteoBiol ® , Tecnoss ® , Giaveno, Italy) used and cited in the selected papers All of them are porcine collagenated xenografts and show high biocompatibility and os teoconductive properties [20,21]. A dedicated product has been developed for every clin ical indication, trying to provide the best handling, granulometry, and consistency, in or der to achieve ideal regenerative results [22]. In particular, the dual-phase heterologou bone matrix granules are composed of a mineral phase and a xenogenic collagen phase which is able to provide the best biocompatibility, a chemical composition similar to au togenous bone, gradual resorption of the bone matrix with the replacement by the newl formed bone at re-entry time, and a high angiogenic potential [23][24][25][26]. These elements ar critical for a successful bone regeneration procedure that sometimes can be further im proved with the association of some of these xenografts.

Description of the Porcine Grafts
Figures 2 and 3 report the characteristics and the clinical applications of the different biomaterials (OsteoBiol ® , Tecnoss ® , Giaveno, Italy) used and cited in the selected papers. All of them are porcine collagenated xenografts and show high biocompatibility and osteoconductive properties [20,21]. A dedicated product has been developed for every clinical indication, trying to provide the best handling, granulometry, and consistency, in order to achieve ideal regenerative results [22]. In particular, the dual-phase heterologous bone matrix granules are composed of a mineral phase and a xenogenic collagen phase, which is able to provide the best biocompatibility, a chemical composition similar to autogenous bone, gradual resorption of the bone matrix with the replacement by the newly formed bone at re-entry time, and a high angiogenic potential [23][24][25][26]. These elements are critical for a successful bone regeneration procedure that sometimes can be further improved with the association of some of these xenografts.

Results
The main effective results for each biomaterial used alone or in combination have been schematically divided and summarized in the tables below [Tables [1][2][3][4][5][6][7][8], on the basis of the clinical indication they have been specifically designed for.

Results
The main effective results for each biomaterial used alone or in combination have been schematically divided and summarized in the tables below [Tables 1-8], on the basis of the clinical indication they have been specifically designed for.

Results
The main effective results for each biomaterial used alone or in combination have been schematically divided and summarized in the tables below [Tables 1-8], on the basis of the clinical indication they have been specifically designed for.    Biocompatibility, bio-resorbability and osteoconductivity: newly formed bone on the xenografts; gradual diffusion of Ca 2+ ions from the biomaterial into the newly forming bone at the interface (biomaterial reabsorption process)        Autologous connective tissue graft provided significant facial soft tissue gain and width augmentation of keratinized mucosa; uneventful healing (6-month follow-up) The biomaterials had different particle sizes, shapes, surface areas, organic material content, and total porosity (mainly submicron pores); Biocoral ® density values were similar to those of hydroxyapatite, while the values of the collagenated samples were lower; most of the samples were hydroxyapatite based The biomaterials were mainly constituted by nanocrystalline apatite mineral, organic collagenous matrix, and water; crystal sizes and specific surfaces areas were similar tothose in bone mineral Coated membranes did not release GO or induce inflammation, and were biocompatible; GO changed stiffness and membrane-AFM tip adhesion, increased the roughness and the total surface exposed to the cells Radunovic M., 2017 [181] LAB Derma Improved proliferation and differentiation of DPSCs, higher compatibility, higher expression of BMP2 and RUNX2, and lower PGE2, COX2, and TNFα levels on GO coated membranes at 14   The controlled release of bioactive growth factors from bone granules promoted bone regeneration in vivo and the increase in VEGF and bFGF markers in vitro Diomede F., 2018 [195] LAB/EXP Evolution CM + EVO membranes + hPDLSCs up-regulated COL5A1, COL16A1, and TGF β1 and down-regulated 26 genes involved in bone regeneration in vitro and showed a better osteogenic ability in calvaria repair in vivo Diomede F., 2016 [196] LAB/EXP Dual-Block DB showed biocompatibility, osteoinductive and osteoconductive properties in vitro and a precocious osteointegration and vascularization in mouse calvaria Diomede F., 2018 [197] LAB/EXP Evolution EVO + PEI-EVs + hPDLSCs showed biocompatibility and an osteogenic potential in vitro and in vivo for the treatment of calvarium and ossification trauma defects Bergmann M., 2020 [198] LAB/EXP Gen-Os ® Complement components secreted by cultured pulp fibroblasts eliminate bacteria and support the early steps of dental tissue regeneration, and those secreted by cultured PLC induced BMMSC recruitment Fernandez M., 2017 [199] LAB/LASL mp3 ® , Evolution Typical HA structure with intraparticle pores; significant porosity, crystallinity, and calcium/phosphate differences; excellent biocompatibility and similarity to natural bone; greater osteoconductivity, but fewer resorption properties for sintered HA xenografts Fernandez M., 2017 [200] LAB/LASL mp3 ® Significant decrease in Ca 2+ /P ratio, high porosity, low crystallinity, low density, large surface area, poor stability, and a high resorption rate in the residual biomaterial of the low-temperature sintered group (6 months after surgery) Biocompatibility and osteoconductive capacity, mild inflammation in the early phase, partial and sequential graft resorption with collagenated porcine bone grafts in both healthy subjects and those with controlled diabetes; similar results in diabetic patients treated with Insulin and strontium ranelate In summary, all the in vitro, experimental, and clinical results described in Tables 1-8 suggested that, during the last 20 years, the OsteoBiol ® collagenated biomaterials have shown reliable outcomes in terms of biocompatibility, morbidity, new bone formation, and bone and soft tissue regeneration, according to expert surgeons' experience.

Discussion
The number of studies reporting surgical techniques for bone regeneration and the clinical effectiveness of bone substitutes and xenografts has greatly increased over the last years, with high predictability and stability of the regenerated alveolar bone ridges [9,18,219]. The treatment of bone defects represents a clinical occurrence that requires optimal management of the threedimensional stability of the grafts and regenerative spaces. In this way, blood-clot stability plays a key role in new bone formation and the morphological restoration of the atrophied bone ridge [220].
The effectiveness of graft implantation is affected by a biunivocal biological relationship between the host tissue and the bone substitutes that has been investigated by numerous histological studies on retrieved biopsies [221].
In many ex vivo studies conducted by using porcine graft specimens, the histologic and histomorphometric evaluations reported newly formed bone in contact with the scaffolds and an evident presence of cells in the osteocyte lacunae [7,24,25,27,222].
This evidence has been corroborated by the clinical success of these biomaterials, which confirmed the histologic and histomorphometric findings and showed an intimate apposition of newly formed bone in contact with the porous porcine-derived biomaterials, especially in maxillary sinus augmentation procedures [28,85,89,90,93,97,[99][100][101]110,111,116,117,119].
In addition, the results obtained from ex vivo and clinical data have been supported by in vitro studies, which demonstrated the osteoblast differentiation and bone regeneration capabilities together with the angiogenic potential of the OsteoBiol ® bone matrix [21,23,26,178,[183][184][185]194,197].
With reference to graft resorption, many studies revealed the nearly complete substitution of membranes and the ongoing resorption of collagenated bone particles within 6 months. Especially, Wachtel et al. [123] reported that the biodegradation of the cortical bone Lamina ® was almost complete after 6 months, with varying degrees of residual graft particles. Cardaropoli et al. [30] confirmed the presence of a marginal residual graft rate (24.5%) of Gen-Os ® biomaterial, covered by Evolution ® collagen membrane to preserve the bone socket, just after 4 months from implant insertion. Additionally, another clinical study [95] reported a high resorption rate of mp3 ® , with 13.55% of residual grafting material after 5 months, that reached 12.3% within 12 months [24]. Considering that the limit for the residual volume of bone grafts for successful implant placement is set at 40% [223], these values are considerably lower.
Regarding the aforementioned residual graft limit, it should be considered that only Apatos Cortical ® showed a higher residue percentage (around 30%) after many years from the surgery, although it stayed within 40%, comparable to the different types of xenografts present in the market [96,224].
However, these histological findings allow for adequate preservation of the grafted volume and do not appear to negatively affect the predictability of regenerative procedures and the survival rate of the dental implant in regenerated sites [225].
Overall, based on the data discussed, it appears clear that, due to the unique properties of these xenografts, an adequate preservation of graft volume and an improved new bone formation have been achieved.
In addition, the literature proved that OsteoBiol ® materials could be used alone or in combination both for the regeneration of bone defects and soft tissue augmentation. For example, in the latter case, membranes, such as Derma, can be used alone as an alternative to connective tissue graft to improve the quality of keratinized tissues [166,[171][172][173][174]. Apatos ® , instead, is a universal filler that can be employed to treat peri-implant defects and two-wall defects [68,74]. Moreover, thanks to its granulometry, Apatos ® fits well in big sockets, e.g., after molar extractions [41]. For this reason, sinus lift procedures (with crestal or lateral access) [85,91] can be performed with Apatos ® as a bone substitute, as well as surgeries for horizontal regenerations. Finally, as an example of a combination of materials, Apatos ® grafts can be protected with Evolution membrane [59] to reach a better ridge preservation compared to non-preserved size.
Although the effectiveness of using these biomaterials has been summarized in the results (Tables 1-8) and discussed in this section, it is necessary to recognize that this narrative review has potential weaknesses. The main limitations include: (i) the manuscript does not contain all the reports in the field of "effectiveness of bone regeneration procedures with collagenated porcine grafts", but only some selected publications that concern OsteoBiol ® biomaterials; (ii) the collected articles come from studies not only conducted by the authors of this review, but also by several other authors; (iii) the manuscript describes the individual works but does not quantify the results, and no statistical analysis is performed here; (iv) the manuscript does not compare the effectiveness of OsteoBiol ® products with other competitors, which are also successfully used for bone and soft tissue regeneration within the craniofacial area. However, our main goal was to summarize the achievements of these specific materials over the years.
Despite these limitations, we can conclude that the 20-year translational research experience showed the safety of these specific porcine bone substitutes and demonstrated their capability to improve the biological response and predictability of regenerative protocols for the treatment of alveolar and maxillofacial defects. For future perspectives, it will certainly be useful to extend the number of included studies, analyze and compare the success rate of each product, and perform longer-term histological and histomorphometric studies in order to better understand the resorption times of all these biomaterials. In this way, a systematic review could be performed to better highlight the advantages of using OsteoBiol ® collagenated porcine bone grafts with respect to other porcine substitutes.

Conflicts of Interest:
The authors declare no conflict of interest.